1. Field of the Invention
The present invention relates to a CPP thin-film magnetic head in which a sense current flows in the thickness direction (direction orthogonal to the film surface) and a method for producing the CPP thin-film magnetic head.
2. Description of the Related Art
Giant magnetoresistive devices (GMR devices) and tunneling magnetoresistive devices (TMR devices), which are used as thin-film magnetic heads, can be broadly divided into a current-in-plane (CIP) mode device, in which a sense current flows in the direction parallel to a surface of a layer constituting the device; and a current-perpendicular-to-plane mode deviate, in which a sense current flows in the direction perpendicular to a surface of a layer constituting the device.
FIG. 11 is a fragmentary sectional view of a traditional CPP thin-film magnetic head. The CPP thin-film magnetic head includes a bottom shield layer 110, a top shield layer 130, the bottom shield layer 110 and the top shield layer 130 being disposed at a predetermined interval, a thin-film magnetic head element 120 opposite a surface of a storage medium and between the bottom and top shield layers 110 and 130, and an insulating layer 140 interposed between the bottom and top shield layers 110 and 130 and disposed behind the thin-film magnetic head element 120 in the height direction. The top shield layer 130 is separated into a first top shield sublayer 131 on the thin-film magnetic head element 120 and a second top shield sublayer 132, the second top shield sublayer 132 being disposed behind the first top shield sublayer 131 in the height direction and conductively connected to the bottom shield layer 110 via a contact hole 141 in the insulating layer 140. Shield underlying layers (not shown) are provided directly below the respective bottom shield layer 110 and the top shield layer 130.
Japanese Unexamined Patent Application Publication Nos. 2002-74936 and 2002-157711 and International Publication No. WO97/44781 (equivalent: PCT Japanese Translation Patent Publication No. 11-509956) are disclosed below. As indicated by the arrow in FIG. 11, a sense current I flows from the first top shield sublayer 131 to the second top shield sublayer 132 through the thin-film magnetic head element 120 and the bottom shield layer 110. Alternatively, the sense current I flows from the second top shield sublayer 132 to the first top shield sublayer 131 through the bottom shield layer 110 and the thin-film magnetic head element 120. The first top shield sublayer 131 and the second top shield sublayer 132 function as passages for the sense current I. In such a CPP thin-film magnetic head including the bottom shield layer 110 and the top shield layer 130 both functioning as electrodes, to reduce a resistance that does not contribute to an element output and the output noise of the element due to an change in the resistance, it is necessary to be free of any oxide layer at interfaces between the thin-film magnetic head element 120 and the bottom shield layer 110 and between the thin-film magnetic head element 120 and the top shield layer 130. Thus, in forming the thin-film magnetic head element 120 on the bottom shield layer 110 and in forming the top shield layer 130 on the thin-film magnetic head element 120, pretreatment is typically conducted to remove a surface oxide layer by, for example, etching.
In the pretreatment before formation of the top shield layer 130, a surface oxide film on the thin-film magnetic head element 120 and a surface oxide film on the bottom shield layer 110 exposed at the contact hole 141 in the insulating layer 140 are removed by etching at the same time. In this manner, since the surface of the bottom shield layer 110 has already been exposed to air at previous steps (for example, a step of forming the thin-film magnetic head element 120), the surface oxide layer on the bottom shield layer 110 is thicker than that of the surface oxide layer on the thin-film magnetic head element 120. Thus, to completely remove the surface oxide layer on the bottom shield layer 110, more than the usual amount of etching is required. However, an increase in the amount of etching for the complete removal of the surface oxide layer on the bottom shield layer 110 results in the deeply etched surface of the thin-film magnetic head element 120, thus causing great damage to the element. Therefore, a thick cap layer, which is the uppermost layer of the thin-film magnetic head element 120, must be provided, thereby preventing a reduction in the interval between the shield layers. Formation of the cap layer composed of a material having oxidation resistance permits minimization of the amount of etching of the thin-film magnetic head element 120. A reduction in the amount of etching in order to avoid the damage of the thin-film magnetic head element 120 results in insufficient removal of the surface oxide layer of the bottom shield layer 110, thereby destabilizing a contact resistance between the bottom shield layer 110 and the second top shield sublayer 132. Furthermore, a resistance that does not contribute to the element output may increase to reduce the element output. Formation of the bottom shield layer 110 composed of a material, for example, ruthenium, having oxidation resistance reduces the amount of etching of the bottom shield layer 110 exposed at the contact hole 141, thus solving the problem above. In view of magnetic shielding effect and the like, it is difficult to use the above-described material having oxidation resistance as the shield material in the present circumstances. This is because such a material, for example, ruthenium, having oxidation resistance does not have magnetic properties and does not exhibit the shield effect. Nowadays, there is no magnetic material having the shield effect and in which when the magnetic material is exposed to oxygen (air), the thickness of the resulting surface oxide layer is comparable to that of the surface oxide layer on the thin-film magnetic head element 120.